Putting the top on

Right! Now you are going to put a top on this car. You will detach the windows later so for now you'll just build the basic shell. Begin by going into "Polygon" mode and select these two polys from the hood of the car.

Hold down shift and drag the polys to the roof area. When a dialog box appears, select "Clone to Element" and then click OK. Make sure that you also drag the polys upwards in the left viewport so they are properly positioned at the height of the roof.

Now start building polys towards the back as shown in the pictures below. Position vertices as shown. You will notice that not all of the blueprints will line up properly at this stage. This is fine as long as the differences are not too severe. You will also notice that there is an edge missing in the roof section to join with the back of the car. This is easily fixed by making the cut shown with a yellow line. Weld vertices in green circles.

Create the three rows of polys shown below.

Shift+drag the edges in red and then move the vertices to the positions shown by the green arrows and then weld them there.

At this point you should have what can be seen below.

Well, now would be a good time to add a "Meshsmooth" modifier to see how the shape looks so far. Click the "Modifier List" drop-down menu and select "Meshsmooth" from the list. Set iterations to 2. Hit "M" to bring up the material editor. Click on the material you used on your mesh if it's not already selected. Click on the "2-Sided" checkbox under "Shader Basic Parameters" to make the material double-sided. Your mesh should look like this at this point (see left).

Closing off the top of the shell

Now, you need to create a poly for the front side window. Go into "Polygon" mode and click on the button labeled "Create" under the stack. Now start with the vertex shown in red and click the four vertices shown in an anti-clockwise direction until a new poly is created.

Extrude the edges shown in the picture.

Now extrude the edge as as shown by the red line. Weld the vertex shown in the green circle to the corresponding one on the rest of the car mesh. Don't worry about the two vertices shown by the green arrows. There will be a gap in the mesh but that's ok because we are going to detach the mesh later.

Create the two cuts shown below:

Shift+drag the edge in red and then move the vertices to the positions shown by the green arrows and then weld them there.

Shift+drag the edge in red and then position vertices as shown. Make the cut shown by the yellow line and then weld vertices in green circles.

Continue shift-dragging the red-marked edges:

There is a small area of the front fender that we forgot to create earlier on so we can quickly do that now. Simply select all the edges in red and shift+drag them downwards. Position the vertices as shown.

This is what the mesh should look like with smoothing on at this point.
Note the little gap that I mentioned earlier.

Now at this point you have the basic shell of the car. It's now time to start adding the little details that will turn it into a Fiat 500.